Thanks for the great feedback, guys!
After further examination and clarification of copyright opinion, here's the link for the Webmineral Lawsonite page;
webmineral.com/data/Lawsonite.shtml and Mindat:
www.mindat.org/min-2353.htmlI really like the Webmineral page for the cool Java applet displaying the crystallography. My simple reason for not displaying links, or quoting text, is ...
I live in California, the State of Litigation.
Besides, you guys have the name, a search is easy to do.
*lol*
Back on track with the discussion:
First, I understand the "it's just a rock" opinions, but the purpose of this RTH section is discussions of material identification, isn't it?
Being a miner, my aim is to sell the rock, but to sell it, "Inquiring minds want to know." Everybody asks, "Well, what is it?" Commercial cutters and brokers won't buy the material without identification, because the Market demands explanations, and the end customer wants "provenance."
Additionally, when it comes to rocks and geology, I'm a big kid. I bubble with excitement at discussions of petrological details, even though I'm, at best, a "cowboy geologist." Never sat in a classroom, but love the science.
And there's always that guy, with his buddies, who wants to know EVERYTHING about the rock, so it pays to know it all.
The identification was of 2 specific examples of top quality material.
The mineral constituents vary widely, but we're using Gem Lawsonite to refer to the whole range of similar material, in a multitude of colors.
Further studies will be performed as funds allow.
Now to discuss cutting characteristics:
Like any lapidary material, there are numerous grades and styles of Gem Lawsonite. (For more on that name, see the thread on Blue G in the Carving section.) These are based both on material integrity and level of inclusion, and color and saturation of color.
We classify the
cuttability by these general grades:
C grade
- C is for "crap." This is the friable, fragmented, barely cuttable marginal material that we're stockpiling to try the Emer-genC & sodium silicate stabilization technique on, someday. We've gotten to the place where we can pick these out in initial cleaning.
Not currently for sale.
B grade
- B is good but fractured, best for tumbling or small cabs. When slabbed, lines of iron oxide or clay tend to cause parting. Nodules are suitable for carving, slabs should be dropped from waist height to induce parting before trimming to cab or bead blank.
These are the main materials in our $1 per pound MFRB's.
B+ grade
- B+ is less fractured and less likely to part in trimming.
A grade
- A is solid, and may show fully healed fractures. Healed fractures look fragile, but if they survive dropping the slab, they'll survive daily wear.
"Top" grade
- The best! Solid, with the highest degree of translucent material and color saturation. May show healed fractures filled with blue silica. We drop
all the Top slabs before packing them, to assure cutters of best return.
Styles -
blue granite - Looks like blue granite, but better. B to A grade.
green granite - greener material, possibly chlorite or epidote as colorant. Often somewhat softer material.
Robin's Egg - Robin's Egg blue, with deeper blue patterns, and sometimes, green-gold spots. Looks like a real robin's egg! This is one of the Top grades.
blue moss - a good, saturated blue, with contrasting mossy patterns, often in several colors.B to Top grade.
Delft blue - sky to powder blue-green, with dark Delft blue moss. B to Top grade.
Black & Blue - Black body color, with blue features, from fine blue veins to discrete crystal forms. Occurs in a range of hues, and usually features abundant secondary minerals. B to Top grade.
Cutters guide:
Gem Lawsonite slabs easily and evenly, due to it's micro-crystalline structure. We use water cooled tile saws with a little surfactant to window and slab, and get great blade life.
Depending on the level of amphibole, pyroxene and other inclusions, cutting can start as low as 60 mesh diamond if the slab has a smooth surface texture. Rougher (sandy) material should be started as high as 220.
Sand through the usual succession of grits, and don't worry if it appears to undercut. That's normal for the heavily included styles, and should even out at 600 mesh. You should also get a velvet polish at 600. As with most materials, the higher the final mesh, the brighter the final polish.
I like sanding with silicon carbide belts and disks. As they wear, the tendency of "hard" diamond wheels to cause pulling of amphibole inclusions is greatly reduced. Past the grinding stage, Nova type diamond tools or silicon carbide have produced the best result for me.
For final polishing, various polishes have been used. We've used tin oxide, cerium oxide, various aluminum oxides and straight diamond.
We've also found that response to particular compound varies from nodule to nodule, and that sometime we have to settle for a velvet polish.
We're going to be trying a vinegar/water spray to see if changing the PH of the polish will help. This makes sense, since this tends to be a very alkaline rock, high in calcium. I've read that alkalinity can inhibit the action of polishing agents, and would love your informed opinions.
The best polish that I've achieved came by sanding through 14,000 Nova diamond, and polishing on medium density felt with tin oxide.
The best I've seen was achieved by Ron Martinez, working with a flex-shaft and accessories to 100,000 diamond, then cerium oxide on hard felt bobs.
Ron's opinion was that cerium was best if high mesh diamond was used, creating a really smooth surface to polish. He got a mirror polish with cerium, where for me the same material would only haze with cerium after 14,000 diamond.
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Mel, thanks for the great input! You're right, we thought that it might be a glaucophane conglomerate, with secondary silicification (agatization).
I was sure that it had to be a deep subduction mineral, and outlined my theories with geologists from local colleges and the USGS. They've helped me to fill in the gaps all through the process, though there was a wide range of opinion as to the majority mineral, and the cause of the blue coloration.
Opinions ranged from jadeite to pumpellyite, and I didn't even
hear of Lawsonite until the GIA results came back. The typical alteration of the hydrous calcium aluminum sorosilicate Lawsonite into Anorthite through dehydration in (near) surface conditions made the verdict a real surprise. That's why I use the term "un-usual" in reference to this material.
Happily, we're getting reports of similar material from other sites on the west coast of North America. Details are quite preliminary and private, but they're sure to be reported here when cutting studies and mineral analysis have been performed.
The conglomerate nature of the rock can be a challenge, but less often than you might think. This is due to what I theorize was a secondary subduction, with infiltration of hydrous alkaline SiO
2 gel (Quartz) under enormous pressure. This effectively sealed and stabilized the Lawsonite after partial alteration to Feldspar, working in concert with the fact that Lawsonite
expands as it cools ("freezes").
As rockhounds who've pounded on unbroken nodules with 3 lb. sledges have found, the best nodules just sit back and say, "You talkin' to me?"
It's
TOUGH!The rule of thumb is, if it powders, it's not top material.
As stated above, I've no formal schooling, just field work and 30+ years of voracious reading. So, any silly notions will be cheerfully discarded when convincing data is presented to debunk them!
};D
That's it for the moment, lapidaries!
Kris